More about the microbiome

John DiTraglia M.D.


The microbiome is the collection of bacteria that live in your guts. There are many more of them than there are human cells in your body. These little creatures collectively have exponentially more genes than do human cells. We have talked about how the microbiomes we carry can influence obesity and type 2 diabetes and there is a new review article about this maybe most modifiable risk factor of all.

Facts about the microbiome:

– Human genes affect the composition of gut microbiota.

– Gut microbiota genes affect the expression of human genes.

– Gut microbiota affect each other.

– Diet affects all this.

– About 90 percent of gut bacteria are in two classes: Bacteroides and Firmicutes. Firmicutes help you absorb more calories than Bacteroides. Obese humans have more Firmicutes, as do obese rodents. But it is unlikely that a single species of bacteria plays a dominent role.

– Gut microbiota from obese mice and from lean mice were planted in germ free lean mice all of whom had the same caloric intake. The mice in the obese microbiota transplant group got fat: the mice receiving microbiota from lean mice stayed lean.

– Mice who are maintained with germ-free guts stay lean. Putting in the germs but not changing the diet increases body fat by 60% and can lead to diabetes.

– Mice that get gastric bypass surgery and lose weight change their gut micobiota populations. Thase bacteria transplanted into new mice caused them to lose weight but not as much as the gastric bypass did in the donor mice.

– When obese people lose weight their gut microbiota changes to that of lean people. When they gain back the lost weight their populations switch back. So this works both ways. The microbiome may be a reflection of obesity and leanness as well as a cause of it.

– Somebody did a study in human twin pairs one of whom was obese. The micobiota form these pairs was planted in germ-free newborn mice. The mice with the obese twin microbiota got fat and the mice with the lean twin microbiota stayed thin. Housing the mice together after a time resulted in all the mice getting thin. Why didn’t the obese humans get thin? I guess they don’t share germs as well as mice do.

Studies in humans can also be done by cleaning out the bowels with laxatives and then planting various microbiomes but the results are mixed and transient and there is wide individual variability so far. Dissecting the issues will be a challenge in humans. But new technologies that allow rapid, inexpensive DNA analyzing will provide a tool to understand how the microbiome might effect health.


John DiTraglia M.D.

John DiTraglia M.D. is a Pediatrician in Portsmouth. He can be reached by e-mail- or phone-354-6605.

John DiTraglia M.D. is a Pediatrician in Portsmouth. He can be reached by e-mail- or phone-354-6605.


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